Heavy Metals Content of Common Tubers from Selected Farm Locations in Enugu North District, South East, Nigeria

Abstract

The concentration of heavy metals (Cd, Pb, Ni, As, Cr, Mn, Cu, and Zn) in sweet potato (Ipomoea batatas), yam (Dioscorea ssp), and cassava (Manihot esculenta) in four farm locations in some local government areas of Enugu North District was determined. Samples were prepared following standard procedure and digested with a 5:1:1 mixture of trioxonitrate (V) acid, tetraoxosulphate (VI) acid, and perchloric acid as previously reported. Metal concentration was determined using Atomic Absorption Spectrophotometer (Perkin Elmer 1100B model). The range of heavy metals concentration recorded for sweet potato in the four farm locations were 60.26±2.30-312.66±31.24 mg/kg, 20.06±1.27-40.55±4.08 mg/kg, 12.60±2.00-32.06±3.20 mg/kg, 8.20±3.00-15.00±1.07 mg/kg, 0.05±0.07-0.80±1.27 mg/kg, 0.07±0.42-0.18±0.42 mg/kg, 0.01±0.20-0.09±0.03 mg/kg and 0.02±0.07-0.03±0.08 mg/kg respectively for Mn, Ni, Cu, Zn, Cr, Pb, As and Cd while the range in yam was 18.46±2.05-380.20±10.97 mg/kg, 44.20±4.99-66.30±3.87 mg/kg, 17.80±2.18-56.08±6.73 mg/kg, 12.00±2.00-42.30±0.06 mg/kg, 0.01±0.32-0.42±0.27 mg/kg, 0.02±0.07-0.20±0.12 mg/kg, 0.04±2.03-0.10±0.00 mg/kg and 0.01±0.07-0.08±0.47 mg/kg for Mn, Cu, Zn, Ni, Cr, Pb, As and Cd respectively. In cassava, the concentration range was 74.20±10.97-312.20±31.20 mg/kg, 14.20±1.29-38.22±6.07 mg/kg, 10.88±3.03-32.00±0.70 mg/kg, 3.20±0.20-11.20±1.09 mg/kg, 0.01±0.20-0.18±1.27 mg/kg, 0.02±0.03-0.12±0.07 mg/kg, 0.01±0.03-0.10±0.07 mg/kg and 0.03±0.00-0.05±0.42 mg/kg for Mn, Ni, Zn,Cu, Cr, Pb, Cd and As respectively. While Cd was not detected in farm location B and D in all the tuber samples, arsenic was detected in all the samples except in cassava cultivated in farm location B. All the heavy metals analyzed were each below the World Health Organization (WHO) permissible concentration except chromium which was slightly higher than the recommended limit of 0.05 mg/kg. Apart from 0.80±1.27 mg/kg Cr recorded for sweet potato cultivated in location C, the concentration of chromium in all the tubers were below the China’s State Environmental Protection Administration (SEPA) permissible limit of 0.5 mg/kg. Hence, risk assessment of Cr intake was recommended to ascertain the level of human exposure to Cr through the consumption of these tubers in the study area